490 THE VOYAGE OF H.M.S. CHALLENGER. 



as determining the later development of two to four or more radii in the different genera 

 of Porodiscida. 



1. Axodiscus stylophorus, n. sp. 



Ring circular, with two equal semicircular chambers, connected with the central chamber by 

 two opposite radial beams, which are prolonged outside into two strong conical spines. 

 Dimensions. Diameter of the ring O05, of the central chamber O'OIG. 

 Habitat. Central Pacific, Station 266, depth 2750 fathoms. 



2. Axodiscus triradiatus, n. sp. 



Eing regular, triangular, equilateral, connected with the central chamber by three equidistant 

 radial beams, which are prolonged outside into three short conical spines. (Differs from Archidisciis 

 trioniscus in the possession of marginal spines.) 



Dimensions. Diameter of the ring O04, of the central chamber O'OIS. 



Habitat. Central Pacific, Station 267, depth 2700 fathoms. 



3. Axodiscus staurophorus, n. sp. 



Eing regular, square, connected with the central chamber by four radial beams, which lie 

 opposite in pairs in two perpendicularly crossed axes, and are prolonged outside into four delicate 

 cylindrical spines. 



Dimensions. Diameter of the ring 0'045, of the central chamber 0'015. 



Habitat. North Pacific, Station 244, depth 2900 fathoms. 



4. Axodiscus hexagonus, n. sp. 



Eing regular, hexagonal, connected with the central chamber by six radial beams at equal 

 distances, which are prolonged outside into six strong pyramidal spines. 

 Dimensions. Diameter of the ring 0'06, of the central chamber O'OIS. 

 Habitat. Central Pacific, Station 271, depth 2425 fathoms. 



5. Axodiscus trigonus, n. sp. 



Eing regular, triangular, equilateral, connected with the central chamber by six radial beams of 

 alternating length and distance ; therefore three smaller (perradial) chambers (with denser and 

 darker network) alternating with three larger (interradial) chambers (with looser and finer network). 

 On the margin three strong conical radial spines, arising in the radius of the larger chambers. 

 (Differs from Archidiscus pyloniscus, PL 48, fig. 11, mainly in the strong angular spines on the three 

 corners of the triangular shell.) 



Dimensions. Diameter of the ring 0'05, of the central chamber 0'014. 



Habitat. South Pacific, Station 296, depth 1825 fathoms. 



